There have conventionally been known applicators which impact a microneedle for administering active components transdermally, so as to apply the microneedle to a skin. For example, the following Patent Literature 1 discloses a self-actuating applicator having a housing, a piston moveable within the housing, and a cap. In this self-actuating applicator, when a spring 40 is compressed so as to store a biasing force, release catches 38 link with a top 19a of an inner cup 14 and piston stop 18, thereby securing a piston 30. Thereafter, when a user exerts a downward force on an outer cup 20, the release catches 38 bend inward and disengage from the piston stop 18, so as to actuate the piston 30, which presses a patch.